The present invention relates to planetary transmissions and, more particularly, to planetary transmissions having three planetary gearsets and five torque-transmitting mechanisms to establish at least six forward speed ratios and one reverse speed ratio.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission, and a differential or final drive mechanism. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times as the transmission ratios are interchanged. The number of forward speed ratios that are available in a transmission determines the number of ratio interchanges that can occur and therefore the number of times the engine torque range can be repeated.
Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point, during cruising, other than the most efficient point. Therefore, manually shifted (countershaft transmissions) were the most popular.
With the advent of three and four speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improve the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration.
It has been suggested that the number of forward speed ratios be increased to five and even six speeds. This has been accomplished in many heavy truck powertrains. Six speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978; U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000; U.S. Pat. No. 5,106,352 issued to Lepelletier on Apr. 21, 1992; and U.S. Pat. No. 5,599,251 issued to Beim and McCarrick on Feb. 4, 1997.
Six speed transmissions offer several advantages over four and five speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ six-speed transmissions, such as Polak, passenger cars are still manufactured, for the main part, with three and four speed automatic transmissions, and relatively few five or six speed devices due to the size and complexity of these transmissions. The Polak transmission provides six forward speed ratios with three planetary gearsets, two clutches, and three brakes. The Koivunen and Beim patents utilize six torque transmitting devices including four brakes and two clutches to establish the six forward speed ratios and one reverse ratio. The Lepelletier employs three planetary gearsets, three clutches and two brakes to provide six forward speed ratios and one reverse ratio. One of the planetary gearsets in Lepelletier is positioned and operated to establish two input members (unity and a reduction speed) for the remaining two planetary gearsets.
It is an object of the present invention to provide an improved family of six-speed transmissions having three planetary gearsets.
In one aspect of the present invention, the transmissions incorporate three planetary gearsets that are controlled by five selectively engageable torque-transmitting mechanisms to provide at least six forward speed ratios and one reverse speed ratio between an input shaft and an output shaft.
In another aspect of the present invention, each of the planetary gearsets has first, second, and third members.
In yet another aspect of the present invention, the first and second members of the first planetary gearset are continuously connected with respective first and second members of the second planetary gearset by respective interconnecting members.
In still another aspect of the present invention, the third member of the second planetary gearset is continuously connected with a first member of the third planetary gearset through a continuous connecting member.
In yet still another aspect of the present invention, the input shaft is continuously connected with one of the members of the planetary gearsets and the output shaft is continuously connected with another member of the planetary gearsets.
In a further aspect of the present invention, the five torque-transmitting mechanisms include three rotating type torque-transmitting mechanisms and two stationary type torque-transmitting mechanisms.
In a yet further aspect of the present invention, the first of the stationary torque-transmitting mechanisms selectively connects a member of the first or third planetary gearset with a stationary member, such as a transmission case.
In yet still a further aspect of the present invention, a second of the stationary torque-transmitting mechanisms selectively connects a member of the first, second or third planetary gearset, or one of the interconnecting members with a stationary transmission member.
In another aspect of the present invention, a first of the rotating type torque-transmitting mechanisms selectively connects a member of the first or second planetary gearset or one of the fixed interconnections with a member of the third planetary gearset.
In yet another aspect of the present invention, a second of the rotating torque-transmitting mechanisms selectively connects a member of the first or second planetary gearset or one of the interconnecting members with either the input shaft, the output shaft, or a member of the third planetary gearset.
In yet still another aspect of the present invention, a third of the rotating torque-transmitting mechanisms selectively interconnects a member of one of the planetary gearsets with either the input shaft, the output shaft, or another member of one of the planetary gearsets.
In a further aspect of the present invention, the five torque-transmitting mechanisms are selectively engageable in combinations of two to establish six at least forward speed ratios and one reverse speed ratio between the input shaft and the output shaft.
In yet still a further aspect of the present invention, each of the planetary gearsets includes a sun gear, a ring gear, and a planet carrier assembly member.
In a still further aspect of the present invention, the planet carrier assembly member can be of either the single pinion type, wherein one pinion gear meshes with both the ring gear and the sun gear, or a compound or double pinion type, wherein intermeshing pinion gears mounted on the planet carrier assembly mesh with the sun gear and ring gear, respectively.